All the way through Scream 4, I was itching for a freeze-frame of Hayden Panettiere's hairdo, so that I could give it an in-depth examination. What the hell was it? Some kind of demi-pompadour with the curlicues glued flat? I suspect that if you were to poke at it, it would be rock-solid, like a Ken doll coiffure. I think it's great they gave her short hair. But did it have to be so weird?

Then again, short hair invariably seems weird in a Hollywood where flowing locks are the norm. Even Demi Moore, who rocked the pixie cut in Ghost, now sports a poker-straight curtain. Hilary Swank goes long between androgyny trims for Boys Don't Cry or Amelia. Who is known for their short hair nowadays? Halle Berry? Shannyn Sossamon? We're edging into C-list territory here. When Emma Watson and Carey Mulligan chopped theirs off, it was considered news; archive photos of Jean Seberg and Twiggy were duly trotted out for comparison, as if to underline the novelty value.

For the record, I love long hair. If mine weren't so baby-fine, I would definitely grow it so I could have a big plait, like the damsels in a King Arthur book I had as a girl. But, being saddled with the wrong sort of piliferous gene, I'm always on the lookout for short crops similar to mine on screen. They are, of course, rare, because long, lustrous tresses are one of the major signifiers of femininity. One of the first things a girl does when disguising her gender is cut her hair, like Katharine Hepburn in Sylvia Scarlett (one of the loveliest crops in movies) or Barbra Streisand ("Forgive me, Papa!") in Yentl.

Short hair on female characters is rarely permitted to exist in its own right. It's a statement, a sign of playing men at their own game: for Keira Knightley, when she swaps modelling for bounty hunting in Domino; for Moore, with her military buzz-cut in GI Jane. Getting chopped is seldom something female characters do of their own volition. It deprives them of a formidable weapon, and, instead of giving them masculine strength, only emphasises their helplessness. Even in Rosemary's Baby, when Mia Farrow announces, "I've been to Vidal Sassoon" (her husband's sarky reply: "Don't tell me you paid for that"), she's unwittingly adding the finishing touch to her own martyrdom.

For the close crop is a station of the coiffe en route to immolation. Maria Falconetti looks suitably gamine at the start of The Passion of Joan of Arc, but it's still not sufficiently martyrish for her inquisitors, who insist on further shearing. Seventy years and many Joans later, Milla Jovovich's experience of modelling for L'Oréal stands her in good stead in The Messenger, when she takes a sword to her braid yet miraculously ends up with the chicest of medieval pudding-bowls, with highlights.

When women have their hair cropped on screen, it's usually because they're under some sort of compulsion or duress. The short haircut is humiliating punishment, meted out to inmate Eleanor Parker in Caged, or to Monica Bellucci, condemned for being the village slut, in Malèna. On other occasions, it's a religious gesture: Audrey Hepburn has hers ritually snipped away in The Nun's Story (though, like the other Hepburn, she always did look cuter with short hair), while Julie Andrews's sensible ex-convent pageboy renders The Sound of Music sexless.

It's a small step from boyish crop to baldness, which may in real life signify Britney-style breakdown, but in the movies more often means alien (Star Trek: The Motion Picture), monster (Splice) or homicidal maniac (Blue Sunshine). It's seen as martyrdom to their art when female actors go the whole hairless hog, like Meryl Streep in Sophie's Choice, Samantha Morton in Minority Report or Natalie Portman in V for Vendetta.

But the consensus is that long hair is prettier, and prettiness is a prerequisite for female actors and the characters they play in all but a handful of movies. So however weird Panettiere's haircut, the fact that she's neither a nun, nor a prisoner, nor pretending to be a man, almost makes Scream 4 worthwhile all on its own.